This invention relates to a new method of scouring and chemically processing wool or other like fibre in a modified scour in order to produce scoured fibres very much improved in respect of a number of important quality parameters. This process is for brevity and convenience referred to as xe2x80x9cSuperscouringxe2x80x9d.
It has been recognised by the inventors for several years that the dull appearance of wool is related in large part to the presence in the wool of iron staining. It has also been recognised by the inventors that this internal co-ordinated iron can be removed by a process involving extraction of the wool with an acid solution, at a pH of not more than 3, preferably 2.0-3.0, in the presence of a metal sequestering agent such as ethylene diamine tetra-acetic acid (EDTA).
The inventors demonstrated several years ago that wool so extracted was capable of achieving a brightness improvement of some 4-6 Y units. However, this technology was for several reasons not capable of being effectively carried out within conventional woolscours. Exploiting this technology has hitherto required a double-pass processing operation through a conventional set of process bowls. This invention details alternative procedures that can be integrated into a single continuous process operation.
Peroxide bleaching is a well-known adjunct to conventional wool scouring in New Zealand and elsewhere. The usual process involves passage of the wool through a hot bowl (invariably the final bowl in the train) containing from 1-10 g/l of hydrogen peroxide, with high pressure squeezing, and entry to a wool dryer where most of the bleaching occurs (although some may continue in the baled wool). However, this form of peroxide bleaching has a major disadvantage in that when the wool is dyed, peroxide residues present in the fibre initiate yellowing reactions which cause the substrate colour of the product being dyed often to be poorer than the original unbleached wool. This phenomenon is dubbed xe2x80x9ccolour reversionxe2x80x9d.
The inventors and their colleagues demonstrated some years ago that colour reversion may be prevented by pretreating the wool prior to dyeing with a suitable reducing agent such as sodium bisulphite or sodium dithionite. These reducing agents destroy the peroxidic residues, and thereby prevent colour reversion. Such a reducing step is not possible in a conventional scour but can be readily achieved in the proposed configuration of attached FIGS. 1(a to d), or other variants of machine layouts suitable for xe2x80x98Superscouringxe2x80x99.
The inventors have found in other related technology for carpet yarn scouring that residual soil on wool may be removed through the combined actions of detergents and dispersing agents. However, in conventional wool scouring the use of dispersants, though often promoted, is not normally cost effective because of the levels of suspended solids contamination of the liquors and the inherent dispersing potential of the suint salts in the more contaminated bowls.
The invention therefore provides in a wool or the like fibre scour at least one of the following:
(a) a scouring process wherein the fibres are subjected to an acid extraction process to remove absorbed iron, and thereby to greatly improve the brightness (Y tristimulus value) of the fibres.
(b) a scouring process wherein a bleaching process is carried out in a bowl or pad part way through the wet process, following by drying, rewetting, and chemical reduction, therefore stabilising the bleached colour to prevent subsequent reversion in the dyebath.
(c) a scouring process wherein scoured clean fibres are dried and dusted, and then reimmersed in liquors containing detergents and dispersants, thereby effectively removing extra amounts of residual dirt.
(d) a scouring process in which, by two separate stages of wet processing, residual grease and residual pesticide levels can be greatly reduced, thereby minimising dangers of market resistance associated with traces of animal-remedy pesticides.
Alternatively or in addition the scouring process can involve drying the wool at both an intermediate and final stage, in which the drying operations can be conveniently and economically carried out by combining them within one integrated drying module.
The invention also provides:
(a) a scoured wool produced by the means of (a)-(d) which presents to the yarn spinner or processor a product offering superior colour and processing performance and freedom from iron-related discoloration problems in wet processing.
(b) a scoured wool also produced thereby that contains less dust and residual soil and thereby offers to the processors advantages of a safer working environment, and improved processing performance.
(c) a process whereby, by both improvements in chemical processing and plant design, all the above benefits of (a)-(d) may be achieved cost-effectively in a single pass through a machine of modest linear extent, compact arrangement, and reasonable cost.
This invention allows these improved qualities to be achieved concurrently in a single pass through a substantially revised configuration of scouring machinery components.
The applicant specifically considers there is novelty in some of the individual chemical processing steps, and in the combination of chemical processing steps within the complete operation to achieve specific results, and for aspects of the equipment in which the process is carried out.
The applicant believes there is novelty for the particular sequence and layout of plant components, including the utilisation if desired of a double-pass dryer configuration.
The particular quality improvements provided by the modified process are:
major improvements in the brightness of scoured wool, as measured by its Y tristimulus value, measured on wool in the xe2x80x98as-isxe2x80x99 state as it comes from the scour. On good-quality New Zealand crossbred fleece wools these increases may be as high as 8-9 units in Y, compared to conventionally scoured wool.
stability of the enhanced colour of the wool to subsequent dyeing, in contrast to conventional bleaching processes, where much of the colour benefit is lost by a yellowing process occurring during dyeing.
very large reductions (on a proportionate basis) of residual grease levels on the scoured wool, down to virtually negligible remaining levels of superficial woolgrease (as distinct from internal wool lipids), which in turn mean that the levels of residual lipophilic ectoparasiticides on the wool are sufficiently reduced to comply with pesticide content regulations.
very substantially reduced contamination of the wool by finely divided residual soil particles, thereby producing not only a brighter wool but one which avoids downstream processing problems associated with residual dirt.
a wool that is comparatively dust free compared to conventionally scoured wool.
a wool that is substantially reduced in its iron content, both as to the iron associated with residual dirt, and the iron that is chemically absorbed and bound within the fibre.
The methods by which each of these improvements may be achieved within proposed machinery configurations are described in turn in the following sections.
The applicant proposes an efficient and logistically acceptable plant configuration in which this process can be incorporated into a single process pass.
The specific requirements which enable this chemical process to be carried out with acceptable efficiency and consistency are that the wool must be in a quite clean state before being acid-treated, that the levels of suspended matter in the bowls must be very low, to avoid redeposition on the wool, and that the levels of dissolved ionic material (predominantly suint salts) carried forward into the acid treatment bowl are very low. These requirements are achieved in the plant configuration described below and shown in FIGS. 1(a to d), and in alternative layouts which incorporate similar overall wet processing stages and intermediate drying and dusting stages.
While acid extraction considerably improves the Y tristimulus value, the Z tristimulus value is improved somewhat less, so that the perceived yellowness of the wool also increases. This disadvantage may be eliminated, with further enhancement of both Y and Z, by the second aspect of colour improvement as described below.